Eu2+-activated aluminates nanobelts, whiskers, and powders, methods of making the same, and uses thereof

ABSTRACT

Embodiments of the present disclosure relate to visible luminescent phosphors, visible luminescent nanobelt phosphors, methods of making visible luminescent phosphors, methods of making visible luminescent nanobelt phosphors, mixtures of visible luminescent phosphors, methods of using visible luminescent phosphors, waveguides including visible luminescent phosphors, white light emitting phosphors, and the like.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional applicationentitled, “Eu²⁺-Activated Aluminates Nanobelts, Whiskers, and Powders,Methods of Making the Same, and Uses Thereof,” having Ser. No.61/309,140, filed on Mar. 1, 2010, which is entirely incorporated hereinby reference.

GOVERNMENT SUPPORT

This invention(s) was made with government support under Grant No.: NSFDMR0955908, which was awarded by the National Science Foundation. Thegovernment has certain rights in the invention(s).

BACKGROUND

Luminescent materials, which underwent almost 100 years' research anddevelopment, are currently indispensable in many important applicationsincluding fluorescent lighting, display devices, X-ray imaging,scintillators, and biological imaging [Adv. Funct. Mater. 13: 511; Yen,W. M., Weber, M. J. Inorganic Phosphors: Compositions, Preparation andOptical Properties. 2003, CRC Press LLC]. The luminescent materials usedin these applications are generally in the form of powders. Recently, aseries of oxide and nitride luminescent materials, such as ZnO, SnO₂ andGaN, were made into one-dimensional (1-D) nanowires and nanobelts thatcan be used as the building blocks for miniaturized nanophotoniccircuits [Science 305: 1269]. Such nanophotonic circuits have thefunctions of light creation, routing and detection, laying the groundfor the fabrication of highly integrated light-based devices such asoptical computers. Due to the limited optical performance of ZnO, SnO₂and GaN (such as limited luminescent colors and defect-relatedemission), however, further development of nanowires circuitry needs newtypes of luminescent nanowires that should have rich luminescent colorsand emit characteristic light. Rare-earth (RE)-activated phosphors withdiversiform luminescence apparently meets this material need.

RE-activated phosphors are one of the most important families ofluminescent materials. In RE-activated phosphors, the RE ions areusually doped into the hosts in either trivalent (RE³⁺) or divalent(RE²⁺) states. Most of the doped RE³⁺ ions have characteristicatomic-like emission spectra, which are attributed to the 4f^(n)→4f^(n)intraconfigurational transitions, due to the well-shielded 4f shell. TheRE²⁺-activated phosphors, in contrast, typically exhibit broad emissionbands, which are generally attributed to the parity-allowed4f^(n-1)5d→4f^(n) interconfigurational transitions whose wavelengthsdepend strongly on the host lattice.

RE²⁺-activated phosphors, particularly Eu²⁺-activated phosphors, arereceiving increasing attention for their tunable band-like emission andbroad excitation range, as well as their many important practicalapplications. For example, the emissions from Eu²⁺ ions in differenthosts can be tuned from near-UV to red, while the excitation can beextended from blue light to even the X-ray region [Res. Rep. 23: 201].The tunable and broad emission and excitation bands of theEu²⁺-activated phosphors could fill up the spectral gaps in the emissionspectrum of current white phosphor-converted LEDs (pc-LEDs) to improvetheir color quality for general illumination [Proc. SPIE 3938: 30]. Thedefect-related charge trapping phenomenon followed by normal 4f⁶5d→4f⁷transitions in some Eu²⁺-activated phosphors has led to such importantapplications as information storage, long persistent luminescence,electroluminescence, and high-energy radiation detection. Besides thenormal 4f⁶5d→4f⁷ transition, some Eu²⁺-doped alkaline earth compoundsalso show an extremely broad and red-shifted anomalous emission bandoriginated from a impurity-trapped exciton (ITE) state, which isconstructed by a hole on the impurity and a trapped conduction electronon the nearby lattice sites [Phys. Rev. B 32: 8465].

SUMMARY

Embodiments of the present disclosure relate to visible luminescentphosphors, methods of making visible luminescent phosphors, mixtures ofvisible luminescent phosphors, methods of using visible luminescentphosphors, waveguides including visible luminescent phosphors, whitelight emitting phosphors, and the like.

An embodiment of the visible luminescent phosphors includes, amongothers, an europium aluminate phosphor having a material having theformula: (M_(z)Eu_(1-z)O)_(x)(Al₂O₃)_(y), wherein M=Ba, Sr or acombination thereof; and 0≦z≦0.99, 1≦x≦5, and 1≦y≦5.

An embodiment of the method of making a phosphor nanobelt includes,among others, mixing an amount of each of Eu₂O₃ and Al₂O₃ with an amountof either of SrO or BaO, ground it with an amount of graphite powder toform a mixture; and heating the mixture to about 1350-1550° C. for about1-3 hours under about 1-50 Torr of flowing argon to form a phosphornanobelt.

An embodiment of the method of making a phosphor whisker, among others,includes: mixing an amount of each of Eu₂O₃ and Al₂O₃ with an amount ofeither of SrO or BaO, ground it with an amount of graphite powder and acatalyst selected from the group consisting of: Fe₂O₃, NiO, SiO₂, andGeO₂, to form a mixture; and heating the mixture to about 1350-1550° C.for about 1-3 hours under about 1-50 Torr of flowing argon to form aphosphor whisker.

An embodiment of the method of making a phosphor powder, among others,includes: mixing an amount of each of Eu₂O₃ and Al₂O₃ with an amount ofeither of SrO or BaO, ground with an amount of graphite powder to form amixture; and heating the mixture alongside an amount of Al₂O₃ powder, toabout 1350-1550° C. for about 1-3 hours under about 1-50 Torr of flowingargon to form a phosphor powder.

An embodiment of the waveguide, among others, includes: a europiumaluminate phosphor having a material of formula:(M_(z)Eu_(1-z)O)_(x)(Al₂O₃)_(y), wherein M=Ba, Sr, or a combinationthereof; and 0≦z≦0.99, 1≦x≦5, and 1≦y≦5.

An embodiment of the white light emitting phosphor mixture, amongothers, includes: (EuO)(Al₂O₃)₃, (EuO)(Al₂O₃), and (EuO)₄(Al₂O₃)₅.

An embodiment of the white light emitting phosphor mixture, amongothers, includes: (Sr_(0.9)Eu_(0.1)O)(Al₂O₃)₃,(Sr_(0.9)Eu_(0.1)O)(Al₂O₃), and (Sr_(0.9)Eu_(0.1)O)₄(Al₂O₃)₅.

An embodiment of the white light emitting phosphor mixture, amongothers, includes: (Ba_(0.75)Eu_(0.25)O)(Al₂O₃)₃,(Ba_(0.99)Eu_(0.01)O)(Al₂O₃), (Ba_(0.99)Eu_(0.01)O)₄(Al₂O₃)₅, and(Ba_(0.75)Eu_(0.25)O)₄(Al₂O₃)₅.

The above brief description of various embodiments of the presentdisclosure is not intended to describe each embodiment or everyimplementation of the present disclosure.

Rather, a more complete understanding of the disclosure will becomeapparent and appreciated by reference to the following description andclaims in view of the accompanying drawings. Further, it is to beunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects of the present disclosure will be more readilyappreciated upon review of the detailed description of its variousembodiments, described below, when taken in conjunction with theaccompanying drawings.

FIG. 1 is the schematic diagram of a tube furnace system used tosynthesize europium aluminate, strontium europium aluminate, and bariumeuropium aluminate, nanobelts, whiskers and powders.

FIG. 2 shows the digital images of (a) blue, (b) green, and (c) orangeluminescent europium aluminate nanobelts taken under a digital opticalmicroscope with a 365 nm ultraviolet lamp irradiation.

FIG. 3 shows the digital images of (a) green and (b) orange luminescenteuropium aluminate powders taken under a digital optical microscope witha 365 nm ultraviolet lamp irradiation.

FIG. 4 shows the transmission electron microscope images of (a) blue,(b) green, and (c) orange luminescent europium aluminate nanobelts.

FIG. 5 shows the X-ray diffraction patterns of (a) blue luminescentEuAl₆O₁₀, (b) green luminescent EuAl₂O₄, and (c) orange luminescentEu₄Al₁₀O₁₉ nanobelts and whiskers.

FIG. 6 shows the room-temperature excitation and emission spectra of (a)blue luminescent EuAl₆O₁₀, (b) green luminescent EuAl₂O₄, and (c) orangeluminescent Eu₄Al₁₀O₁₉ nanobelts and powders.

FIG. 7 shows the light generation and propagation on individual (a)orange luminescent Eu₄Al₁₀O₁₀ nanobelt struck by a blue laser beam, (b)blue luminescent EuAl₆O₁₀ nanobelt struck by a focused X-ray beam, (c)green luminescent EuAl₂O₄ nanobelt struck by a focused x-ray beam, and(d) orange luminescent Eu₄Al₁₀O₁₀ nanobelt struck by a focused x-raybeam.

FIGS. 8A and B show the white light generated by the combination of theblue, green, and orange luminescent europium aluminates.

FIG. 9 shows the digital images of (a) blue, (b) green, and (c) yellowluminescent strontium europium aluminate nanobelts taken under a digitaloptical microscope with a 365 nm ultraviolet lamp irradiation.

FIG. 10 shows the digital images of (a) yellow and (b) green luminescentstrontium europium aluminate powders taken under a digital opticalmicroscope with a 365 nm ultraviolet lamp irradiation.

FIG. 11 shows the scanning electron microscope images of (a) blue, (b)green and (c) yellow luminescent strontium europium aluminate nanobeltsand the transmission electron microscope images of (d) blue, (e) greenand (f) yellow luminescent strontium europium aluminate nanobelts.

FIG. 12 shows the scanning electron microscope images of Ge-catalyzed(a) blue and (b, c) yellow luminescent strontium europium aluminatewhiskers.

FIG. 13 shows the X-ray diffraction patterns of (a) blue luminescentSr_(0.9)Eu_(0.1)Al₆O₁₀, (b) green luminescent Sr_(0.9)Eu_(0.1)Al₂O₄, and(c) yellow luminescent Sr_(3.6)Eu_(0.4)Al₁₀O₁₉, nanobelts, whiskers, andpowders.

FIG. 14 shows the room-temperature excitation and emission spectra of(a) blue luminescent Sr_(0.9)Eu_(0.1)Al₆O₁₀, (b) green luminescentSr_(0.9)Eu_(0.1)Al₂O₄, and (c) yellow luminescentSr_(3.6)Eu_(0.4)Al₁₀O₁₉, nanobelts, whiskers, and powders.

FIG. 15 shows the digital images of (a) blue, (b) green, (c) yellow, and(d) red luminescent barium europium aluminate nanobelts taken under adigital optical microscope with a 365 nm ultraviolet lamp irradiation.

FIG. 16 shows the digital images of (a) yellow and (b) red luminescentbarium europium aluminate powders taken under a digital opticalmicroscope with a 365 nm ultraviolet lamp irradiation.

FIG. 17 shows the scanning electron microscope images of (a) blue, (b)green, (c) yellow, and (d) red luminescent, barium europium aluminatenanobelts.

FIG. 18 shows the X-ray diffraction patterns of (a) blue luminescentBa_(0.75)Eu_(0.25)Al₆O₁₀, (b) green luminescent Ba_(0.99)Eu_(0.01)Al₂O₄,(c) yellow luminescent Ba_(3.96)Eu_(0.04)Al₁₀O₁₉, and (d) redluminescent Ba₃EuAl₁₀O₁₉ nanobelts and powders.

FIG. 19 shows the room-temperature excitation and emission spectra of(a) blue luminescent Ba_(0.75)Eu_(0.25)Al₆O₁₀, (b) green luminescentBa_(0.99)Eu_(0.01)Al₂O₄, (c) yellow luminescentBa_(3.96)Eu_(0.04)Al₁₀O₁₉, and (d) red luminescent Ba₃EuAl₁₀O₁₉nanobelts and powders.

FIG. 20 illustrates prototype white LED packages. FIGS. 20 a to cillustrate digital images of three prototype white LED packages (W1, W2and W3) operated under forward bias current of 20 mA. FIG. 20 dillustrates emission spectra of the three prototype white LED packagesunder forward bias current of 20 mA. FIG. 20 e illustrates thechromaticity coordinates on CIE 1931 diagram.

DETAILED DESCRIPTION

Before the present disclosure is described in greater detail, it is tobe understood that this disclosure is not limited to particularembodiments described, and as such may, of course, vary. It is also tobe understood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting, since the scope of the present disclosure will be limited onlyby the appended claims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range, is encompassed within the disclosure. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges and are also encompassed within the disclosure, subjectto any specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the disclosure.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the present disclosure, the preferredmethods and materials are now described.

All publications and patents cited in this specification are hereinincorporated by reference as if each individual publication or patentwere specifically and individually indicated to be incorporated byreference and are incorporated herein by reference to disclose anddescribe the methods and/or materials in connection with which thepublications are cited. The citation of any publication is for itsdisclosure prior to the filing date and should not be construed as anadmission that the present disclosure is not entitled to antedate suchpublication by virtue of prior disclosure. Further, the dates ofpublication provided could be different from the actual publicationdates that may need to be independently confirmed.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the presentdisclosure. Any recited method can be carried out in the order of eventsrecited or in any other order that is logically possible.

Embodiments of the present disclosure will employ, unless otherwiseindicated, techniques of chemistry, physics, and the like, which arewithin the skill of the art.

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how toperform the methods and use the probes disclosed and claimed herein.Efforts have been made to ensure accuracy with respect to numbers (e.g.,amounts, temperature, etc.), but some errors and deviations should beaccounted for. Unless indicated otherwise, parts are parts by weight,temperature is in ° C., and pressure is at or near atmospheric. Standardtemperature and pressure are defined as 20° C. and 1 atmosphere.

Before the embodiments of the present disclosure are described indetail, it is to be understood that, unless otherwise indicated, thepresent disclosure is not limited to particular materials, reagents,reaction materials, manufacturing processes, or the like, as such canvary. It is also to be understood that the terminology used herein isfor purposes of describing particular embodiments only, and is notintended to be limiting. It is also possible in the present disclosurethat steps can be executed in different sequence where this is logicallypossible.

As used herein, the term “comprising,” which is synonymous with“including” or “containing,” is inclusive, open-ended, and does notexclude additional unrecited elements or method steps.

It must be noted that, as used in the specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a compound” includes a plurality of compounds. In thisspecification and in the claims that follow, reference will be made to anumber of terms that shall be defined to have the following meaningsunless a contrary intention is apparent.

Discussion:

Embodiments of the present disclosure relate to visible luminescentphosphors, methods of making visible luminescent phosphors, mixtures ofvisible luminescent phosphors, methods of using visible luminescentphosphors, waveguides including visible luminescent phosphors, whitelight emitting phosphors, and the like. The visible luminescentphosphors (also referred to as “phosphors”) of the present disclosureare rare-earth-activated luminescent aluminates. In particular,embodiments of the phosphors disclosed herein are Eu²⁺-activatedluminescent europium aluminates, Eu²⁺-activated luminescent strontiumeuropium aluminates, and Eu²⁺-activated luminescent barium europiumaluminates. The phosphors can be efficiently excited by a wide range ofwavelengths from blue light to ultraviolet, X-ray, and to e-beam.Embodiments of the present disclosure are capable of emitting light inany visible color. The wavelength of emission can be adjusted byselectively adjusting the manufacturing parameters, such as temperatureand/or pressure. In particular, the wavelength for emission bandsassociated with these phosphors is about 400 nm to 900 nm. Themorphology of the visible luminescent phosphors can include forms suchas a nanobelt, a whisker, a powder, or a combination thereof.Embodiments of the phosphors can be used in LEDs and nanophotoniccircuitry (e.g., waveguides), for example.

In general, the phosphors of the present disclosure include a family ofcompositions generally described by: (M_(z)Eu_(1-z)O)_(x)(Al₂O₃)_(y),wherein M=Ba, Sr, or a combination thereof; and 0≦z≦0.99, 1≦x≦5, and1≦y≦5.

In an embodiment, the Eu²⁺-activated luminescent europium aluminates(EAO) disclosed herein are (EuO)_(x)(Al₂O₃)_(y), where 1≦x≦5 and 1≦y≦5,and in particular, x=1 or 4 and y=1, 3, or 5. Under excitation, theEu²⁺-activated luminescent europium aluminates can emit intense andbroad bands in blue, green, and orange spectral regions, where thespecific spectral regions can be selected by adjusting the manufacturingprocess. Specific embodiments of the europium aluminates can include:(EuO)(Al₂O₃)₃ [i.e., EuAl₆O₁₀], (EuO)(Al₂O₃) [i.e., EuAl₂O₄], and(EuO)₄(Al₂O₃)₅ [i.e., Eu₄Al₁₀O₁₉]. Under excitation at room temperature,EuAl₆O₁₀, EuAl₂O₄, and Eu₄Al₁₀O₁₉ exhibit intense band emissions in blue(emission peak=about 425 nm, FWHM=30 nm), green (emission peak=about 525nm, FWHM=88 nm), and orange (emission peak=about 645 nm, FWHM=153 nm)spectral regions, respectively.

In an embodiment, the Eu²⁺-activated luminescent strontium europiumaluminates (SEAO) disclosed herein are represented by the generalformula: (Sr₂Eu_(1-z)O)_(x)(A₂O₃)_(y), where 0.1≦5≦0.99, 1≦x≦5, and1≦y≦5. Under excitation, the Eu²⁺-activated luminescent strontiumeuropium aluminates can emit intense and broad bands in blue, green, andyellow spectral regions, where the specific spectral regions can beselected by adjusting the manufacturing process. In an embodiment, theEu²⁺-activated luminescent strontium europium aluminates can include:(Sr_(0.9)Eu_(0.1)O)(Al₂O₃)₃, (Sr_(0.9)Eu_(0.1)O)(Al₂O₃), and(Sr_(0.9)Eu_(0.1)O)₄(Al₂O₃)₅, with respective luminescent colors (underexcitation at room temperature) of blue (emission peak=about 426 nm,FWHM=35 nm), green (emission peak=about 520 nm, FWHM=87 nm), and yellow(emission peak=about 600 nm, FWHM=144 nm).

In an embodiment, the Eu²⁺-activated luminescent barium europiumaluminates (BEAO) disclosed herein are represented by the generalformula: (Ba_(z)Eu_(1-z)O)_(x)(Al₂O₃)_(y), where 0.1≦z≦0.99, 1≦x≦5, and1≦y≦5. Under excitation, the Eu²⁺-activated luminescent barium europiumaluminates can emit intense and broad bands in blue, green, yellow andred spectral regions, where the specific spectral regions can beselected by adjusting the manufacturing process. In an embodiment, theEu²⁺-activated luminescent barium europium aluminates can include:(Ba_(0.75)Eu_(0.25)O)(Al₂O₃)₄, (Ba_(0.99)Eu_(0.01))(Al₂O₃),(Ba_(0.99)Eu_(0.01)O)₄(Al₂O₃)₅, and (Ba_(0.75)Eu_(0.25)O)₄(Al₂O₃)₅ withrespective luminescent colors (under excitation at room temperature) ofblue (emission peak=about 433 nm, FWHM=44 nm), green (emissionpeak=about 500 nm, FWHM=73 nm), yellow (emission peak=about 595 nm,FWHM=131 nm) and red (emission peak=732 nm, FWHM=157 nm).

In an embodiment, the Eu²⁺-activated luminescent strontium europiumaluminates (SEAO) disclosed herein are (Sr_(z)Eu_(1-z)O)_(x)(Al₂O₃)_(y),wherein 0.1≦z≦0.99, 1≦x≦5, and 1≦y≦5, and in particular, z=0.9, x=1 or4, and y=1, 3 or 5. Under excitation, the Eu²⁺-activated luminescentstrontium europium aluminates can emit intense and broad bands in blue,green, and yellow spectral regions, where the specific spectral regionscan be selected by adjusting the manufacturing process. In anembodiment, the Eu²⁺-activated luminescent strontium europium aluminatescan include: (Sr_(0.9)Eu_(0.1)O)(Al₂O₃)₃ [i.e., Sr_(0.9)Eu_(0.1)Al₆O₁₀],(Sr_(0.9)Eu_(0.1)O)(Al₂O₃) [i.e., Sr_(0.9)Eu_(0.1)Al₂O₄], and(Sr_(0.9)Eu_(0.1)O)₄(Al₂O₃)₅ [i.e., Sr_(3.6)Eu_(0.4)Al₁₀O₁₉]. Underexcitation at room temperature, Sr_(0.9)Eu_(0.1)Al₆O₁₀,Sr_(0.9)Eu_(0.1)Al₂O₄, and Sr_(3.6)Eu_(0.4)Al₁₀O₁₉ emit intense andbroadband emissions in blue (emission peak=about 426 nm, FWHM=35 nm),green (emission peak=about 520 nm, FWHM=87 nm), and yellow (emissionpeak=about 600 nm, FWHM=144 nm) spectral regions, respectively.

In another embodiment, Eu²⁺-activated phosphors can be prepared bycombining both BaO and SrO as alkaline-earth containing startingmaterials.

In an embodiment, the Eu²⁺-activated luminescent barium europiumaluminates (BEAO) disclosed herein are (Ba_(z)Eu_(1-z)O)_(x)(Al₂O₃)_(y),where 0.1≦z≦0.99, 1≦x≦5, and 1≦y≦5, and in particular, z=0.75 or 0.99,x=1 or 4, and y=1, 3 or 5. Under excitation, the Eu²⁺-activatedluminescent barium europium aluminates can emit intense and broad bandsin blue, green, yellow, and red spectral regions, where the specificspectral regions can be selected by adjusting the manufacturing process.In an embodiment, the barium europium aluminates can include:(Ba_(0.75)Eu_(0.25)O)(Al₂O₃)₃ [i.e., Ba_(0.75)Eu_(0.25)Al₆O₁₀],(Ba_(0.99)Eu_(0.01)O)(Al₂O₃) [i.e., Ba_(0.99)Eu_(0.01)Al₂O₄],(Ba_(0.99)Eu_(0.01)O)₄(Al₂O₃)₅ [i.e., Ba_(3.96)Eu_(0.04)Al₁₀O₁₉], and(Ba_(0.75)Eu_(0.25)O)₄(Al₂O₃)₅ [i.e., Ba₃EuAl₁₀O₁₉]. Under excitation,Ba_(0.75)Eu_(0.25)Al₆O₁₀, Ba_(0.99)Eu_(0.01)Al₂O₄,Ba_(3.96)Eu_(0.04)Al₁₀O₁₉, and Ba₃EuAl₁₀O₁₉ emit intense and broadbandemissions in blue (emission peak=about 433 nm, FWHM=44 nm), green(emission peak=about 500 nm, FWHM=73 nm), yellow (emission peak=about595 nm, FWHM=131 nm) and red (emission peak=about 774 nm, FWHM=218 nm)spectral regions, respectively.

In an embodiment, the europium-activated luminescent nanobelts can befabricated by a thermal evaporation-based technique in a well-controlledtube furnace system. A certain amount of the source oxides, such asEu₂O₃, Al₂O₃, SrO, or BaO, are mixed and ground with graphite powder.The approximate ratios of the components and the approximate value ofvarious processing conditions are described in Tables 1, 3, and 4, whereapproximate is equivalent to the term “about”, as defined herein. Themixture is then heated in a tube (e.g., an alumina tube) at about1350-1550° C. for about 1-3 hours under about 1-50 Torr of flowing inertgas (e.g., argon). The inert flow rate, e.g., argon flow rate, can beabout 50-150 standard cubic centimeter per minute (sccm). The nanobeltsare grown on the alumina substrates located at the downstream positionof the processing tube. In an embodiment, the nanobelt has a rectangularcross-section. The nanobelt can have a length of about 10 micrometers to2 millimeters, a width of about 200 to 600 nm, and a thickness of about50 to 300 nm.

In an embodiment, the europium-activated luminescent whiskers disclosedherein are generally fabricated in the presence of a catalyst. Thecatalysts can include metals Fe and Ni, or semiconductors Ge and Si.Like the nanobelt, the whiskers are grown by thermal evaporation of amixture of source oxides (e.g., Eu₂O₃, Al₂O₃, SrO, and/or BaO), catalystoxide (e.g., Fe₂O₃, NiO, SiO₂, or GeO₂), and graphite powders. Theapproximate ratios of the components and the approximate value ofvarious processing conditions are described in Tables 1, 3 and 4, whereapproximate is equivalent to the term “about”, as defined herein. Thewhiskers are grown on the alumina substrates located at the downstreamposition of the alumina processing tube via a mechanism calledvapor-liquid-solid (Wagner, R. S., Ellis, W. C. (1964),“Vapor-liquid-solid mechanism of single crystal growth”, Appl. Phys.Lett. 4: 89). The nanowhiskers are grown on the alumina substrateslocated at the downstream position of the processing tube. Thenanowhiskers can have a diameter of about 0.5 to 5 micrometers andlength of about 0.01 to 0.5 millimeters or up to about 1 millimeter.

In an embodiment, the europium-activated luminescent powders disclosedherein are fabricated by placing additional Al₂O₃ powder adjacent to themixture of source oxides (e.g., Eu₂O₃, Al₂O₃, SrO, or BaO) and graphitepowders. The approximate ratios of the components and the approximatevalue of various processing conditions are described in Tables 1, 3, and4, where approximate is equivalent to the term “about”, as definedherein. The vapor generated from the oxide-graphite mixture reacts withAl₂O₃ to form the luminescent powder at the Al₂O₃ site.

Individually, each of the europium aluminates can be excited by a lightsource and then the europium aluminate emits energy at a wavelength, asmentioned above. The light source can be an e-beam (emissionwavelength≦0.01 nm), an X-ray beam (about 0.01-10 nm), avacuum-ultraviolet light source (e.g., about 112-200 nm from a deuteriumlamp), an ultraviolet light source (e.g., about 250-390 nm from a xenonarc lamp), a laser beam (e.g., about 355 nm from a Nd—YAG laser or about488 nm from an argon laser), LED (e.g., UV LED or blue LED), or acombination thereof.

When excited by an ultraviolet light (e.g., about 250-390 nm), themixture of the three europium aluminates disclosed herein, i.e.,blue-emitting EuAl₆O₁₀, green-emitting EuAl₂O₄, and orange-emittingEu₄Al₁₀O₁₉, can create a D65 daylight illuminant. The D65 illuminantcorresponds roughly to a mid-day sun in Western Europe and North Europe,hence it is also called a daylight illuminant. According to theInternational Commission on Illumination (CIE) “D65 is intended torepresent average daylight and has a correlated color temperature ofapproximately 6500 K”. In a specific embodiment, the three europiumaluminates disclosed herein can therefore be used as the phosphors forwhite pc-LEDs.

When excited by an ultraviolet light (e.g., about 250-390 nm), themixture of the three strontium europium aluminates, i.e., blue-emittingSr_(0.9)Eu_(0.1)Al₆O₁₀, green-emitting Sr_(0.9)Eu_(0.1)Al₂O₄, andyellow-emitting Sr_(3.6)Eu_(0.4)Al₁₀O₁₉, can create a D65 daylightilluminant. In a specific embodiment, the three strontium europiumaluminates disclosed herein can therefore be used as the phosphors forwhite LEDs in particular, pc-LEDs.

When excited by an ultraviolet light (e.g., about 250-390 nm), themixture of the four barium europium aluminates, i.e., blue-emittingBa_(0.75)Eu_(0.25)Al₆O₁₀, green-emitting Ba_(0.99)Eu_(0.01)Al₂O₄,yellow-emitting Ba_(3.96)Eu_(0.04)Al₁₀O₁₉, and red-emittingBa₃EuAl₁₀O₁₉, can create a D65 daylight illuminant. In a specificembodiment, the four barium europium aluminates disclosed herein cantherefore be used as the phosphors for white LEDs in particular,pc-LEDs.

When excited by a blue LED (e.g., about 430-480 nm), the yellow-emittingBa_(3.96)Eu_(0.04)Al₁₀O₁₉ disclosed herein emits intense yellow lightand the mixing of the blue and yellow light creates white light withcolor correlated temperature (CCT)<4000 K and color rendering index(CRI)>80, which is suitable for indoor illumination. The yellow-emittingBa_(3.96)Eu_(0.04)Al₁₀O₁₉ disclosed herein alone can therefore be usedas the phosphor for phosphor-conversion white LEDs (pc-white LEDs) inparticular, for indoor illumination.

When struck by a focused e-beam, an X-ray beam, or a laser beam, intenseblue, green, orange, yellow, or red light is generated and the nanobeltor whisker can function as a waveguide for the propagation and routingof the generated light. Therefore embodiments of the present disclosurecan be used as the building blocks for the construction of nanophotoniccircuitry.

Since the Eu²⁺-activated luminescent aluminates disclosed herein can beexcited by high energy sources (e.g., e-beam, X-ray and vacuumultraviolet), the aluminates may be used as phosphors in plasma displaypanels and scintillating devices.

EXAMPLES

Now having described the embodiments of the present disclosure, ingeneral, the examples describe some additional embodiments of thepresent disclosure. While embodiments of the present disclosure aredescribed in connection with the examples and the corresponding text andfigures, there is no intent to limit embodiments of the presentdisclosure to these descriptions. On the contrary, the intent is tocover all alternatives, modifications, and equivalents included withinthe spirit and scope of embodiments of the present disclosure.

Example 1 Method of Preparation of Luminescent Aluminates Nanobelts,Whiskers, and Powders

Synthesis of luminescent nanobelts: The synthesis is based on thermalevaporation of oxide-graphite powders under controlled conditions in awell-controlled tube furnace system (See FIG. 1). The furnace systemcontains a high-temperature tube furnace with a maximum temperature of1700° C., a high-purity alumina tube with OD of 1.75 inch and ID of 1.5inch, an argon gas supply and control system, a mechanical pump, and apressure monitoring and control system. A certain amount of oxidepowders (Eu₂O₃, Al₂O₃, SrO, or BaO) are mixed and ground with a certainamount (e.g., the approximate ratios of the components and theapproximate value of various processing conditions are described inTables 1, 3, and 4, where approximate is equivalent to the term “about”,as defined herein) of graphite powders. The mixture is placed in analumina crucible that is then inserted into the center of a 1.5 inch IDalumina tube. In this tube furnace system, the temperature, alumina tubechamber pressure, gas flow rate, and evaporation time can be preciselycontrolled and adjusted. Several alumina plates with sizes of about 5-cmlong and 1-cm wide are placed at the downstream region of the aluminatube to act as the nanobelts growth substrates. High-purity argon isused as the carrier gas. Before the heating, the alumina tube is pumpedto about 2×10⁻³ Torr. The furnace is then heated to the reactiontemperature to start the growth. The preferred growth condition is asfollows: furnace temperature, about 1350-1500° C.; argon flow rate,about 50-150 sccm; reaction chamber pressure, about 1-50 Torr;evaporation time, about 1-3 hours. After the reaction, the furnace isnaturally cooled down to room temperature. The functions of the graphitepowder are twofold: (i) carbothermal reduction of the high-melting pointoxide powders to efficiently provide Eu-, Al-, Sr-, or Ba-containingspecies and (ii) retaining a weakly reducing environment in the reactionchamber to make Eu ions in divalent state. The function of the argon gasis to carry the oxide vapor to the downstream region. The temperaturegradient profile (top inset in FIG. 1; the profile was measured when thefurnace temperature is set at 1450° C.) at the furnace hearth area (thearea where the growth substrates are located and growth occurs) plays arole in controlling the product morphology, compositions, crystalstructures, and/or luminescence properties. For example, in growingeuropium aluminates nanobelts, the orange-emitting nanobelts are grownat about 1200-1400° C., while the green-emitting nanobelts are formed atabout 1000-1200° C. (see the bottom inset in FIG. 1; the image was takenunder a 365 nm ultraviolet lamp illumination). Moreover, the propertiesof the products are also determined by the growth parameters, especiallythe relative ratio of the source powders, the argon flow rate, and thereaction chamber pressure.

Synthesis of luminescent whiskers: The synthesis of luminescent whiskersuses the same setup as depicted in FIG. 1. The procedure and parametersare the same as those used for nanobelts synthesis, except that a smallamount (e.g., about 1 mol %) of catalyst oxide powder (e.g., Fe₂O₃, NiO,SiO₂, or GeO₂) is mixed into the oxide-graphite mixture. The whiskersare grown on the alumina substrates. The whisker is characteristic ofhaving a catalyst particle at its tip.

Synthesis of luminescent powders: The synthesis of luminescent powdersuses the same setup as depicted in FIG. 1. The procedure and parametersare the same as those used for nanobelts synthesis, except that acertain amount (e.g., about 0.1 g) of additional Al₂O₃ powder is placeddownstream adjacent to the oxide-graphite mixture (FIG. 1). The Al₂O₃powder reacts with the vapor generated from the oxide-graphite mixtureto form Eu²⁺-containing luminescent powders. The formation ofEu²⁺-containing aluminates powders on the Al₂O₃ powder site does notaffect the growth of nanobelts and whiskers on the downstream aluminasubstrates.

Example 2 Preparation and Characterization of Europium AluminateNanobelts, Whiskers and Powders

The europium aluminate (EAO) nanobelts are prepared by the generalmethod of Example 1. Based on the processing conditions (Table 1), threekinds of EAO nanobelts with luminescence colors (under excitation) ofblue, green, and orange are fabricated. When the Eu₂O₃/Al₂O₃/graphiteratios are about (0.1-1)/(0.1-0.4)/1, orange luminescent EAO nanobeltsare formed in the about 1200-1400° C. region and green luminescent EAOnanobelts are grown in the about 1000-1200° C. region (FIG. 1). Whenmore Al₂O₃ powder is added into the source, the growth of the orange andgreen luminescent EAO nanobelts are suppressed; instead, a third type ofblue luminescent EAO nanobelts are grown in the whole growth region fromabout 1000-1400° C.

TABLE 1 Processing parameters for blue-, green-, and orange- coloremitting europium aluminates nanobelts. Source materials Evaporation Arflow Growth Growth Emission & Mass ratios temperature Pressure ratetemperature duration color (Eu₂O₃/Al₂O₃/graphite) (° C.) (Torr) (sccm)(° C.) (hour) Blue (0.1-1)/(0.5-1)/1 1350-1500 5-50 50-100 1400-1000 1-3Green (0.1-1)/(0.1-0.5)/1 1350-1500 5-50 50-100 1200-1000 1-3 Orange(0.1-1)/(0.1-0.5)/1 1350-1500 5-50 50-100 1400-1200 1-3

In the conditions of growing green and orange luminescent EAO nanobelts,when additional Al₂O₃ powder is placed adjacent to the oxide-graphitemixture, orange luminescent EAO powder is formed at the Al₂O₃ site. Whenthe argon flow rate is increased to about 100-200 sccm, however, greenluminescent EAO powder is formed.

FIG. 2 shows the digital images of (a) blue, (b) green, and (c) orangeluminescent europium aluminate nanobelts taken under a digital opticalmicroscope with a 365 nm ultraviolet lamp irradiation. FIG. 3 shows thedigital images of (a) green and (b) orange luminescent europiumaluminate powders taken under a digital optical microscope with a 365 nmultraviolet lamp irradiation. FIG. 4 shows the transmission electronmicroscope images of (a) blue, (b) green, and (c) orange luminescenteuropium aluminate nanobelts. The nanobelts have widths of about 200 to600 nanometers, thicknesses of about 50 to 300 nm, and lengths of about10 μm to 2 mm.

Quantitative composition analyses using a energy-dispersive X-rayspectroscope (EDS) show that the compositions of the EAO can berepresented by (EuO)_(x)(Al₂O₃)_(y), wherein the x and y values vary fordifferent luminescence color products. For the blue luminescent EAO, thex and y values are 1 and 3, respectively; accordingly, the compositionof the blue luminescent EAO is (EuO)(Al₂O₃)₃, i.e., EuAl₆O₁₀. For thegreen luminescent EAO (including nanobelts and powders), the x and yvalues are 1 and 1, respectively; accordingly, the composition of thegreen luminescent EAO is (EuO)(Al₂O₃), i.e., EuAl₂O₄. For the orangeluminescent EAO (including nanobelts and powders), the x and y valuesare 4 and 5, respectively; accordingly, the composition of the orangeluminescent EAO is (EuO)₄(Al₂O₃)₅, i.e., Eu₄Al₁₀O₁₉.

FIG. 5 shows the X-ray diffraction patterns of (a) blue luminescentEuAl₆O₁₀, (b) green luminescent EuAl₂O₄ (including nanobelts andpowders), and (c) orange luminescent Eu₄Al₁₀O₁₉ (including nanobelts andpowders). The green luminescent EuAl₆O₁₀ can be indexed using theisostructural monoclinic SrAl₂O₄. However, no correspondingisostructural phases are available for the blue luminescent EuAl₆O₁₀ andorange luminescent Eu₄Al₁₀O₁₉ in the ICDD (International Centre forDiffraction Data) database and other commonly available database.

Complementary structural analyses using regular X-ray diffraction,synchrotron X-ray microdiffraction, high-resolution transmissionelectron microscopy, and electron diffraction show that the blueluminescent EuAl₆O₁₀, green luminescent EuAl₂O₄, and orange luminescentEu₄Al₁₀O₁₉ nanobelts have, respectively, tetragonal, monoclinic, andhexagonal crystal structures with new lattice parameters. Table 2 liststhe structural information of the three europium aluminate nanobelts.

TABLE 2 Structural information of europium aluminate nanobelts Emis-sion Chemical Crystal Growth Color Formula Structures Lattice ParametersDirection Blue EuAl₆O₁₀ Tetragonal a = b = 7.77 Å, [110] c = 17.30 Å, α= β = γ = 90° Green EuAl₂O₄ Monoclinic a = 8.44 Å, b = 8.83 Å [010] c =5.16 Å, β = 93.25° Orange Eu₄Al₁₀O₁₉ Hexagonal a = b = 6.154 Å [001] c =10.57 Å α = β = 90°, γ = 120°

The EAO phosphors can be effectively excited by a wide range ofwavelengths ranging from blue light to ultraviolet, X-ray, and toe-beam, and emit intense characteristic blue, green and orange lights ofEu²⁺ ions.

FIG. 6 shows the room-temperature excitation and emission spectra of the(a) blue luminescent EuAl₆O₁₀, (b) green luminescent EuAl₂O₄, and (c)orange luminescent Eu₄Al₁₀O₁₉ nanobelts and powders. The emissionspectra (solid line) are excited by 350 nm ultraviolet light. Theexcitation spectra (dashed line) are monitoring at 430 nm for blueluminescent EuAl₄O₁₀, 530 nm for green luminescent EuAl₂O₄, and 640 nmfor orange luminescent Eu₄Al₁₀O₁₉. The blue luminescence with typicalfull-width at half-maximum (FWHM) is attributed to the localized4f⁶5d→4f⁷ transition of Eu²⁺ active centers. The green luminescence alsooriginates from the 4f⁶5d→4f⁷ transition of Eu²⁺ active centers but hasa larger FWHM, probably due to the formation of a more delocalized Eu²⁺chain in the host. The orange luminescence, in contrast, features anunusual, extremely wide emission band and large stokes shift that arecharacteristic of the anomalous impurity-trapped exciton (ITE)luminescence [J. Phys.: Condens. Mater. 15: 2645].

When an individual EAO nanobelt or whisker is struck by a focusede-beam, an X-ray beam, or a laser beam, intense blue, green or orangelight is generated, and the nanobelt or whisker can also function as awaveguide for the propagation and routing of the generated light.

FIG. 7 shows the light generation and propagation on individual (a)orange luminescent Eu₄Al₁₀O₁₀ nanobelt struck by a blue laser beam, (b)blue luminescent EuAl₆O₁₀ nanobelt struck by a focused X-ray beam, (c)green luminescent EuAl₂O₄ nanobelt struck by a focused X-ray beam, and(d) orange luminescent Eu₄Al₁₀O₁₀ nanobelt struck by a focused X-raybeam. The insert in FIG. 7 a is the magnified image of the emitting tipof the nanobelts. The diameter of the X-ray beam is about 0.5 μm and thepositions of the X-ray beam in FIG. 7 b-d are indicated by white dashedcircles. The images were taken when room light was off.

Since the emission bands of the blue, green, and orange luminescent EAOphosphors cover the whole visible region, the mixture of these threealuminates can provide phosphors for white LEDS, in particular, whitelight pc-LEDs.

FIG. 8 a shows the emission spectra (dashed lines) of the blue, green,and orange luminescent europium aluminates excited by 360 nm ultravioletlight, as well as the combined emission spectrum (solid line) of thesethree emission bands. FIG. 8 b is the related CIE chromaticity diagram,in which the three open triangles respectively represent thechromaticity points of the blue, green and orange luminescentaluminates, and the open circle represents the chromaticity point of thecombined emission. The position of the combined emission is perfectlysuperposed with the position of the standard D65 daylight illuminantwhich has a correlated color temperature of about 6500 K. The solidcurve is the black-body radiation locus.

Example 3 Preparation and Characterization of Strontium EuropiumAluminate Nanobelts, Whiskers and Powders

The strontium europium aluminate (SEAO) nanobelts are prepared by thegeneral method of Example 1. Based on the processing conditions (Table3), three kinds of SEAO nanobelts with luminescence colors (underexcitation) of blue, green, and yellow are fabricated. When theSrO/Eu₂O₃/Al₂O₃/graphite ratios are about (0.5-1)/(0.1-1)/(0.1-0.4)/1,yellow luminescent SEAO nanobelts are formed in the about 1200-1400° C.region and green luminescent SEAO nanobelts are grown in the about1000-1200° C. region. When more Al₂O₃ powder is added into the source,the growth of the orange and green luminescent nanobelts are suppressed;instead, a third type of blue luminescent SEAO nanobelts are grown inthe whole growth region from about 1000-1400° C.

TABLE 3 Processing parameters for blue-, green-, and yellow-coloremitting strontium europium aluminate nanobelts and whiskers. Sourcematerials Evaporation Ar flow Growth Growth Emission & Mass ratiostemperature Pressure rate temperature duration color(SrO/Eu₂O₃/Al₂O₃/graphite) (° C.) (Torr) (sccm) (° C.) (hour) Blue(0.5-1)/(0.1-1)/(0.5-1)/1 1350-1500 5-50 50-100 1400-1000 1-3 Green(0.5-1)/(0.1-1)/(0.1-0.5)/1 1350-1500 5-50 50-100 1200-1000 1-3 Yellow(0.5-1)/(0.1-1)/(0.1-0.5)/1 1350-1500 5-50 50-100 1400-1200 1-3

In the conditions of growing SEAO nanobelts, when a small amount (e.g.,about 1 mol %) of catalyst oxide such as Fe₂O₃, NiO, SiO₂, or GeO₂ isadded into the oxide-graphite mixture, straight SEAO whiskers will begrown with Fe, Ni, Si, or Ge as the catalyst.

In the conditions of growing green and yellow luminescent SEAOnanobelts, when additional Al₂O₃ powder is placed adjacent to theoxide-graphite mixture, yellow luminescent SEAO powder is formed at theAl₂O₃ site. When the argon flow rate is increased to about 100-200 sccm,however, green luminescent SEAO powder is formed.

FIG. 9 shows the digital images of (a) blue, (b) green, and (c) yellowluminescent strontium europium aluminate nanobelts taken under a digitaloptical microscope with a 365 nm ultraviolet lamp irradiation.

FIG. 10 shows the digital images of (a) green and (b) yellow luminescentstrontium europium aluminate powders taken under a digital opticalmicroscope with a 365 nm ultraviolet lamp irradiation.

FIG. 11 shows the scanning electron microscope images of (a) blue, (b)green and (c) yellow luminescent strontium europium aluminate nanobeltsand the transmission electron microscope images of (d) blue, (e) greenand (f) yellow luminescent strontium europium aluminate nanobelts. Thenanobelts have widths of about 200 to 600 nanometers, thicknesses ofabout 50 to 300 nm, and lengths of about 10 μm to 2 mm.

FIG. 12 shows the scanning electron microscope images of Ge-catalyzed(a) blue and (b, c) yellow luminescent strontium europium aluminatewhiskers. The morphological feature of the catalytically grown whiskersis that each whisker terminates with a catalyst particle (see FIG. 12c). The whiskers have diameters of about 0.5 to 5 μm and length of up toabout 1 mm.

Quantitative composition analyses using a energy-dispersive X-rayspectroscope (EDS) show that the compositions of the SEAO phosphors canbe represented by (Sr_(z)Eu_(1-z)O)_(x)(Al₂O₃)_(y), wherein z is a valueof around 0.9 and the x and y values vary for different luminescencecolor products. For the blue luminescent SEAO, the x and y values are 1and 3, respectively; accordingly, the composition of the blueluminescent SEAO is (Sr_(0.9)Eu_(0.1)O)(Al₂O₃)₃, i.e.,Sr_(0.9)Eu_(0.1)Al₆O₁₀. For the green luminescent SEAO (includingnanobelts and powders), the x and y values are 1 and 1, respectively;accordingly, the composition of the green luminescent SEAO is(Sr_(0.9)Eu_(0.1)O)(Al₂O₃), i.e., Sr_(0.9)Eu_(0.1)Al₂O₄. For the yellowluminescent SEAO (including nanobelts and powders), the x and y valuesare 4 and 5, respectively; accordingly, the composition of the yellowluminescent SEAO is (Sr_(0.9)Eu_(0.1)O)₄(Al₂O₃)₅, i.e.,Sr_(3.6)Eu_(0.4)Al₁₀O₁₉.

FIG. 13 shows the X-ray diffraction patterns of (a) blue luminescentSr_(0.9)Eu_(0.1)Al₆O₁₀ (including nanobelts and whiskers), (b) greenluminescent Sr_(0.9)Eu_(0.1)Al₂O₄ (including nanobelts, whiskers andpowders), and (c) yellow luminescent Sr_(3.6)Eu_(0.4)Al₁₀O₁₉ (includingnanobelts, whiskers and powders). The patterns of the blue luminescentSr_(0.9)Eu_(0.1)Al₆O₁₀, green luminescent Sr_(0.9)Eu_(0.1)Al₂O₄, andyellow luminescent Sr_(3.6)Eu_(0.4)Al₁₀O₁₉ are the same as the patternsof the blue luminescent EuAl₆O₁₀, green luminescent EuAl₂O₄, and orangeluminescent Eu₄Al₁₀O₁₉, respectively. The green luminescentSr_(0.9)Eu_(0.1)Al₂O₄ can be indexed as monoclinic SrAl₂O₄. However, nocorresponding isostructural phases are available for the blueluminescent Sr_(0.9)Eu_(0.1)Al₆O₁₀ and yellow luminescentSr_(3.6)Eu_(0.4)Al₁₀O₁₉ in the ICDD database and other commonlyavailable databases.

Complementary structural analyses using regular X-ray diffraction,synchrotron X-ray microdiffraction, high-resolution transmissionelectron microscopy, and electron diffraction show that the blueluminescent Sr_(0.9)Eu_(0.1)Al₆O₁₀, green luminescentSr_(0.9)Eu_(0.1)Al₂O₄, and yellow luminescent Sr_(3.6)Eu_(0.4)Al₁₀O₁₉nanobelts and whiskers have, respectively, tetragonal, monoclinic, andhexagonal crystal structures with new lattice parameters.

The SEAO phosphors can be effectively excited by a wide range ofwavelengths ranging from blue light to ultraviolet, X-ray, and toe-beam, and emit intense characteristic blue, green and yellow lights ofEu²⁺ ions.

FIG. 14 shows the room-temperature excitation and emission spectra ofthe (a) blue luminescent Sr_(0.9)Eu_(0.1)Al₆O₁₀, (b) green luminescentSr_(0.9)Eu_(0.1)Al₂O₄, and (c) yellow luminescentSr_(3.6)Eu_(0.4)Al₁₀O₁₉ nanobelts, whiskers and powders. The emissionspectra (solid line) are excited by 350 nm ultraviolet light. Theexcitation spectra (dashed line) are monitoring at about 430 nm for blueluminescent Sr_(0.9)Eu_(0.1)Al₆O₁₀, about 530 nm for green luminescentSr_(0.9)Eu_(0.1)Al₂O₄, and about 590 nm for yellow luminescentSr_(3.6)Eu_(0.4)Al₁₀O₁₉.

Example 4 Preparation and Characterization of Barium Europium AluminateNanobelts, Whiskers and Powders

The barium europium aluminate (BEAO) nanobelts are prepared by thegeneral method of Example 1. The fabrication of the BEAO compounds isvery sensitive to the processing parameters, especially to the chamberpressure and Ar flow rate. Based on the processing conditions (Table 4),four kinds of BEAO nanobelts with luminescence colors (under excitation)of blue, green, yellow, and red are fabricated. Under the typicalconditions of BaO/Eu₂O₃/A₂O₃/graphite mass ratios of about(0.5-1)/(0.1-1)/(0.1-0.5)/1 and evaporation temperatures of about1350-1500° C., red luminescent BEAO nanobelts are formed when pressureis about 15-50 Torr and Ar flow rate is about 50-60 sccm, yellowluminescent BEAO nanobelts are formed when pressure is about 5-10 Torrand Ar flow rate is about 60-100 sccm, and green luminescent BEAOnanobelts are formed when pressure is about 5-15 Torr and Ar flow rateis about 100-150 sccm. When more Al₂O₃ powder is added into the source,blue luminescent BEAO nanobelts are obtained under a pressure about 5-15Torr and argon flow rate of about 50-100 sccm.

TABLE 4 Processing parameters for blue-, green-, yellow, and red-coloremitting barium europium aluminate nanobelts and whiskers. Sourcematerials Evaporation Ar flow Growth Growth Emission & Mass ratiostemperature Pressure rate temperature duration color(BaO/Eu₂O₃/Al₂O₃/graphite) (° C.) (Torr) (sccm) (° C.) (hour) Blue0.5-1/(0.1-1)/0.5-1/1 1350-1500 5-50  50-100 1400-1000 1-3 Green0.5-1/(0.1-1)/0.1-0.5/1 1350-1500 5-15 100-150 1300-1000 1-3 Yellow0.5-1/(0.1-1)/0.1-0.5/1 1350-1500 5-10  60-100 1300-1200 1-3 Red0.5-1/(0.1-1)/0.1-0.5/1 1350-1500 15-50  50-60 1300-1000 1-3

In the conditions of growing yellow and red luminescent BEAO nanobelts,when additional Al₂O₃ powder is placed adjacent to the oxide-graphitemixture, yellow and red luminescent BEAO powders are formed at the Al₂O₃sites, respectively.

FIG. 15 shows the digital images of (a) blue, (b) green, (c) yellow, and(d) red luminescent barium europium aluminate nanobelts taken under adigital optical microscope with a 365 nm ultraviolet lamp irradiation.

FIG. 16 shows the digital images of (a) yellow and (b) red luminescentbarium europium aluminate powders taken under a digital opticalmicroscope with a 365 nm ultraviolet lamp irradiation.

FIG. 17 shows the scanning electron microscope images of (a) blue, (b)green, (c) yellow, and (d) red luminescent barium europium aluminatenanobelts. The nanobelts have widths of about 200 to 600 nanometers,thicknesses of about 50 to 300 nm, and lengths of about 10 μm to 2 mm.

Quantitative composition analyses using a energy-dispersive X-rayspectroscope (EDS) show that the compositions of the BEAO phosphors canbe represented by (Ba_(z)Eu_(1-z)O)_(x)(Al₂O₃)_(y), wherein z is either0.75 (for blue and red luminescent BEAO) or 0.99 (for green and yellowluminescent BEAO), and the x and y values vary for differentluminescence color products. For the blue luminescent BEAO, z=0.75, x=1,and y=3; accordingly, the composition of the blue luminescent BEAO is(Ba_(0.75)Eu_(0.25)O)(Al₂O₃)₃, i.e., Ba_(0.75)Eu_(0.25)Al₆O₁₀. For thegreen luminescent BEAO, z=0.99, x=1, and y=1; accordingly, thecomposition of the green luminescent BEAO is(Ba_(0.99)Eu_(0.01)O)(Al₂O₃), i.e., Ba_(0.99)Eu_(0.01)Al₂O₄. For theyellow luminescent BEAO (including nanobelts and powders), z=0.99, x=4,and y=5; accordingly, the composition of the yellow luminescent BEAO is(Ba_(0.99)Eu_(0.01)O)₄(Al₂O₃)₅, i.e., Ba_(3.96)Eu_(0.04)Al₁₀O₁₉. For thered luminescent BEAO (including nanobelts and powders), z=0.75, x=4, andy=5; accordingly, the composition of the yellow luminescent BEAO is(Ba_(0.75)Eu_(0.25)O)₄(Al₂O₃)₅, i.e., Ba₃EuAl₁₀O₁₉.

FIG. 18 shows the X-ray diffraction patterns of (a) blue luminescentBa_(0.75)Eu_(0.25)Al₆O₁₀, (b) green luminescent Ba_(0.99)Eu_(0.01)Al₂O₄,(c) yellow luminescent Ba_(3.96)Eu_(0.04)Al₁₀O₁₉ (including nanobeltsand powders), and (d) red luminescent Ba₃EuAl₁₀O₁₉ (including nanobeltsand powders). The green luminescent Ba_(0.99)Eu_(0.01)Al₂O₄ can beindexed as hexagonal BaAl₂O₄ (PDF #72-387). However, no correspondingisostructural phases are available for the blue luminescentBa_(0.75)Eu_(0.25)Al₆O₁₀, yellow luminescent Ba_(3.96)Eu_(0.04)Al₁₀O₁₉,and red luminescent Ba₃EuAl₁₀O₁₉ in the ICDD database and other commonlyavailable database.

Complementary structural analyses using regular X-ray diffraction,synchrotron X-ray microdiffraction, high-resolution transmissionelectron microscopy, and electron diffraction show that the blueluminescent Ba_(0.75)Eu_(0.25)Al₆O₁₀, yellow luminescentBa_(3.96)Eu_(0.04)Al₁₀O₁₉, and red luminescent Ba₃EuAl₁₀O₁₉ nanobeltshave, respectively, tetragonal, hexagonal, and hexagonal crystalstructures with new lattice parameters.

The BEAO phosphors can be effectively excited by a wide range ofwavelengths ranging from blue light to ultraviolet, X-ray, and toe-beam, and emit intense characteristic blue, green, yellow, and redlights of Eu²⁺ ions.

FIG. 19 shows the room-temperature excitation and emission spectra of(a) blue luminescent Ba_(0.75)Eu_(0.25)Al₆O₁₀, (b) green luminescentBa_(0.99)Eu_(0.01)Al₂O₄, (c) yellow luminescentBa_(3.96)Eu_(0.04)Al₁₀O₁₉, and (d) red luminescent Ba₃EuAl₁₀O₁₉nanobelts and powders. The emission spectra (solid line) are excited by350 nm ultraviolet light. The excitation spectra (dashed line) aremonitoring at 430 nm for blue luminescent Ba_(0.75)Eu_(0.25)Al₆O₁₀, 500nm for green luminescent Ba_(0.99)Eu_(0.01)Al₂O₄, 580 nm for yellowluminescent Ba_(3.96)Eu_(0.04)Al₁₀O₁₉, and 730 nm for red luminescentBa₃EuAl₁₀O₁₉.

Since the emission bands of the blue, green, yellow, and red luminescentBEAO phosphors cover the whole visible region, the mixture of these fouraluminates can provide phosphors for white light pc-LEDs. Significantly,because of the wide emission band of the yellow luminescentBa_(3.96)Eu_(0.04)Al₁₀O₁₉ (e.g., about 500 nm to 700 nm), exciting theyellow luminescent Ba_(3.96)Eu_(0.04)Al₁₀O₁₉ alone with a 470 nm blueLED can generate warm white light with CCT<4000 K and CRI>80, which issuitable for indoor illumination.

FIGS. 20 a-c show three prototype white LED packages, labeled as W1, W2and W3, which were fabricated by encapsulating InGaN blue LED chip(λ_(max)=470 nm) with a layer of Ba_(3.96)Eu_(0.04)Al₁₀O₁₉. The colorqualities of the three white LED packages were tuned by adjusting thethickness of Ba_(3.96)Eu_(0.04)Al₁₀O₁₉ layer. The as-fabricated whiteLED packages emit bright white light under forward bias current of 20mA. The white light gets warmer from W1 to W3. FIG. 20 d shows theemission spectra of the three white LED packages. The spectra werenormalized at 470 nm and were offset along y-axis for clarity. For eachspectrum, two emission bands were clearly resolved at 470 nm and 580 nm,corresponding to the emission peaks of blue LED chip and Ba_(3.96)Eu_(0.04)Al₁₀O₁₉, respectively. The relative intensity of yellowemission band increases with the Ba_(3.96)Eu_(0.04)Al₁₀O₁₉ layerthickness from W1 to W3, which results in white light with differentcolor qualities. FIG. 20 e shows the chromaticity coordinates of thethree white lights on Commission Internationale de I'Eclairage (CIE).The three dots indicate the color points of the three white LEDpackages. The solid curve is the Planckian locus. The white light fromW1 is located at (0.359, 0.359) with CCT=4500 K and CRI=81. The whitelight from W2 is located at (0.388, 0.389) with CCT=3900 K and CRI=82.The white light from W3 is located at (0.415, 0.423) with CCT=3500 K andCRI=78. The color quality of W2 perfectly meets the demand for indoorillumination.

The complete disclosures of the patents, patent documents, andpublications cited herein are incorporated by reference in theirentirety as if each were individually incorporated. Variousmodifications and alterations to embodiments of this disclosure willbecome apparent to those skilled in the art without departing from thescope and spirit of this disclosure. It should be understood that thisdisclosure is not intended to be unduly limited by the illustrativeembodiments and examples set forth herein and that such examples andembodiments are presented by way of example only with the scope of thedisclosure intended to be limited only by the claims set forth herein asfollows.

It should be noted that ratios, concentrations, amounts, and othernumerical data may be expressed herein in a range format. It is to beunderstood that such a range format is used for convenience and brevity,and thus, should be interpreted in a flexible manner to include not onlythe numerical values explicitly recited as the limits of the range, butalso to include all the individual numerical values or sub-rangesencompassed within that range as if each numerical value and sub-rangeis explicitly recited. To illustrate, a concentration range of “about0.1% to about 5%” should be interpreted to include not only theexplicitly recited concentration of about 0.1 wt % to about 5 wt %, butalso include individual concentrations (e.g., 1%, 2%, 3%, and 4%) andthe sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within theindicated range. In an embodiment, the term “about” can includetraditional rounding according to significant figures of the numericalvalue. In addition, the phrase “about ‘x’ to ‘y’” includes “about ‘x’ toabout ‘y’”.

Many variations and modifications may be made to the above-describedembodiments. All such modifications and variations are intended to beincluded herein within the scope of this disclosure and protected by thefollowing claims.

What is claimed is:
 1. A method of making a phosphor nanobelt,comprising: mixing an amount of each of Eu₂O₃ and Al₂O₃ with an amountof either of SrO or BaO, ground with an amount of graphite powder toform a mixture; and heating the mixture to about 1350-1550° C. for about1-3 hours under about 1-50 Torr of flowing argon to form a phosphornanobelt.
 2. A method of making a phosphor whisker, comprising: mixingan amount of each of Eu₂O₃ and Al₂O₃ with an amount of either of SrO orBaO, ground with an amount of graphite powder and a catalyst selectedfrom the group consisting of: Fe₂O₃, NiO, SiO₂, and GeO₂, to form amixture; and heating the mixture to about 1350-1550° C. for about 1-3hours under about 1-50 Torr of flowing argon to form a phosphor whisker.3. A method of making a phosphor powder, comprising: mixing an amount ofeach of Eu₂O₃ and Al₂O₃ with an amount of either of SrO or BaO, groundwith an amount of graphite powder to form a mixture; and heating themixture alongside an amount of Al₂O₃ powder, to about 1350-1550° C. forabout 1-3 hours under about 1-50 Torr of flowing argon to form aphosphor powder.
 4. A europium aluminate phosphor comprising: a materialincluding a phosphor selected from the group consisting of: a phosphorhaving the formula (EuO)(Al₂O₃)₃, a phosphor having the formula(Sr_(0.9)Eu_(0.1)O)₄(Al₂O₃)₅, a phosphor having the formula(Ba_(0.99)Eu_(0.01)O)₄(Al₂O₃)₅, and a phosphor having the formula(Ba_(0.75)Eu_(0.25)O)₄(Al₂O₃)₅.
 5. The phosphor of claim 4, wherein whenthe phosphor is (EuO)(Al₂O₃)₃, the phosphor has the characteristic thatit emits intense blue light under excitation.
 6. The phosphor of claim5, wherein the phosphor has a tetragonal crystal structure.
 7. Thephosphor of claim 4, wherein when the phosphor is (EuO)₄(Al₂O₃)₅, thephosphor has the characteristic that it emits intense and broad orangelight under excitation.
 8. The phosphor of claim 7, wherein the phosphorhas a hexagonal crystal structure.
 9. The phosphor of claim 4, whereinwhen the phosphor is (Sr_(0.9)Eu_(0.1)O)₄(Al₂O₃)₅, the phosphor has thecharacteristic that it emits intense and broad yellow light underexcitation.
 10. The phosphor of claim 9, wherein the phosphor has ahexagonal crystal structure.
 11. The phosphor of claim 4, wherein whenthe phosphor is (Ba_(0.99)Eu_(0.01)O)₄(Al₂O₃)₅, the phosphor has thecharacteristic that it emits intense and broad yellow light underexcitation.
 12. The phosphor of claim 11, wherein the phosphor has ahexagonal crystal structure.
 13. The phosphor of claim 4, wherein thephosphor emits a white light when excited by a 430-480 nm blue LED. 14.The phosphor of claim 4, wherein when the phosphor is(Ba_(0.75)Eu_(0.25)O)₄(Al₂O₃)₅, the phosphor has the characteristic thatit emits intense and broad red light under excitation.
 15. The phosphorof claim 14, wherein the phosphor has a hexagonal crystal structure.